Last year, so few people contracted measles in England and Wales that the disease was declared technically “eliminated”. The national MMR (measles mumps rubella) vaccination programme is to thank. But set against this welcome news were some imperfect stats: in England in 2016/17, only 87.6 per cent of children had received both the required doses of the vaccine by their fifth birthday – a drop compared with the previous two years. At least part of the reason was a reluctance among some parents to have their children vaccinated. This is a problem that affects other countries, and other vaccines, too. And it’s troubling, because clusters of unvaccinated or under-vaccinated children are more susceptible to disease outbreaks – indeed, a measles outbreak in Leeds and Liverpool just last year affected unprotected children, providing a reminder why all children should be vaccinated.

In a new paper, published in Nature Human Behaviour, a team led by Avnika Amin at Emory University, US, reveal a previously overlooked explanation for “vaccine hesitancy”, as it’s called – and it’s to do with parents’ basic moral values.

Recent interventions designed to improve childhood vaccination rates have focused on providing parents with facts about vaccines. But while educational campaigns of this kind can be successful in the short term, they can backfire, making some parents even less willing to vaccinate their children than they were before. This makes sense if you consider that parents’ decisions are not based only on the facts, but also on their moral values. By also addressing this influence on parents’ attitudes to vaccination, it may be possible to develop more effective interventions and help increase vaccination rates further.

Our moral values – the extent to which we prioritise loyalty or fairness, for example – are known to guide our decisions and behaviour in other areas, such as climate change and philanthropy. So the researchers reasoned that it made sense to look how they might influence attitudes towards vaccination. To do this, Amin and her colleagues surveyed 1,007 US parents of children aged under 13 about their attitudes to vaccination, and about their moral values, and looked to see if there was a connection between the two.

Almost three quarters of parents fell into the “low hesitancy” category (they didn’t have a problem with vaccines); about 11 per cent were classed as “medium hesitancy” (they expressed concerns about vaccinations and had perhaps delayed their child’s vaccinations as a result); and 16 per cent were classed as “high hesitancy” (they had seriously delayed or even refused vaccinations).

In terms of their moral values, both medium and high-hesitancy parents were twice as likely as low-hesitancy parents to place a high emphasis on “purity” (one of six “moral foundations”, purity is associated with disapproval of acts that are deemed “disgusting” or “unnatural”). The high-hesitancy parents were also twice as likely as low-hesitancy parents to place a strong emphasis on liberty, which involves valuing individual freedom. They were also half as likely endorse obedience to authority. Belief in the importance of fairness (another moral foundation) was not related to vaccine hesitancy, and neither were gender or political ideology.

A second study, using a separate group of 464 parents, validated these findings. But the data from both studies only show a correlation between particular moral standpoints and attitudes towards childhood vaccinations, not a causal link. Nonetheless, the researchers said their results suggest that “health decisions are, to some extent, linked with moral concerns” and that there was promise in exploring the impact of health messages “framed using the moral foundations associated with medium or high hesitancy”.

For example, they suggested an intervention framed in terms of purity might read, “Boost your child’s natural defences against diseases! Keep your child pure of infections – Vaccinate!” A message framed in terms of liberty might read, “Take personal control of your child’s health! Vaccinations can help your child and others be free to lead a happy and healthy life!”